The diaeresis is used to indicate that two vowels are to be pronounced separately as two syllables, rather than as a diphthong or single vowel. In compound words, a hyphen - is used to separate the syllables instead.

The umlaut diacritic is used only in words of German origin, such as föhn.

Formerly used, in the letter "u", formed "ü", in the syllables "qüe", "qüi", "güe" and "güi". In these syllables, the letter "u" without a trema would be silent; with the trema it would have the sound of the semivowel/w/.